This invention relates to an automobile suspension bridging each wheel of a vehicle to a vehicle body.
Automobile suspensions of strut type and double wishbone type have been generally known and have been put into practical use.
In the strut type suspension, a fictitious kingpin axis as a rotary shaft for steering the wheel is a straight line which connects a connecting point of an upper end of a damper device and a vehicle body and a connecting point of a lower arm and a wheel support member. The fictitious kingpin axis cannot be desirable upon the performance of the vehicle. In detail, upon the performance of the vehicle, the ideal fictitious kingpin axis passes slightly inboard than a center line in a car width direction of the wheel on a rotating center line of the wheel, and passes slightly outboard than the center line in the car width direction of the wheel at a contact face of the wheel to the ground so that the kingpin offset is slightly negative. However, the fictitious kingpin axis of the strut type suspension is inclined inboard of the ideal fictitious kingpin axis.
On the other hand, in the double wishbone type suspension, the fictitious kingpin axis is a straight line which connects a connecting point of an upper arm and the wheel support member and a connecting point of the lower arm and the wheel support member. This appropriate setting of the connecting points brings the fictitious kingpin axis to almost the ideal one. However, the double wishbone type suspension requires each two points for the connecting the upper arm and the lower arm to the vehicle body in order to support horizontal load affecting to the wheel, which restricts the layout of the other parts. Particularly, when the double wishbone type suspension is used as a front-wheel suspension in an FF (front-engine front-drive) type automobile, the layout is severely restricted. The strut type suspension has no problem on the layout because of no upper arm.
There have been many automobile suspensions proposed for solving the problem with both advantages of strut type and double wishbone type suspensions. Typical conventional examples are explained below, referring to the respective references.
The first example is disclosed in Japanese Patent Application Laying Open Gazette No. 2-220904. The suspension in this example is basically of improved double wishbone type. The suspension is constructed in such a fashion that the upper arm is composed of a single link member and a lower end of the damper device is connected to the lower arm so that the damper device also supports the load effecting the wheel. According to this suspension, with the only one connecting point of the upper arm to the vehicle body, the parts can be arranged more freely.
The second conventional example is disclosed in German Patent Application Laying Open Gazette No. DE 3,839/463A1. In this suspension, the upper arm is constructed by a single link member as well as in the first example, and the lower end of the damper device is connected to the wheel support member. Thus, the layout is free from restriction.
The third conventional example is disclosed in Japanese Patent Application Laying Open Gazette No. 1-136804. The suspension of this example is basically, also, of improved double wishbone type, wherein an intermediate member is provided between the wheel support member and the upper arm to be connected to the lower end of the damper device, and the wheel support member is pivotally fitted via a ball joint to the intermediate member to allow the upper arm to swing only in a vertical direction.
These examples, however, have respective problems. In detail:
In the first conventional example, since the lower end of the damper device is connected to an intermediate part in the car width direction of the lower arm, it is required to increase a force (damping force) generated by the damper device so as to correspond to a lever ratio with respect to an external force in the vertical direction affecting to the wheel at bumping and rebounding of the wheel. This involves increase size and weight of the damper device and the lower arm connected thereto. Further, in the FF type automobile, a drive shaft extends in the car width direction on the rotating center line of the wheel. For avoiding an interference between the drive shaft and the damper device connected to the lower arm, it is required to provide between the lower end of the damper device and the lower arm a forked connecting member through which the drive shaft is put. Since the connecting member fully receives the force generated by the damper device, the connecting member must have large rigidity, which causes enlarged scale. Consequently, the weight increases further.
In the second conventional example, since an arm part for connecting to the damper device is required to be formed at the wheel support member , the construction becomes complicated and the weight is increased. Further, since the lower end of the damper device extends downward further than the rotating center line of the wheel, it is required in the FF type automobile to avoid the interference between the damper device and the drive shaft, which causes restriction of the layout. In addition, the fictitious kingpin axis is inclined upwardly, inboard, so as to be far from the ideal Fictitious kingpin axis.
In the third example, since the wheel support member and the intermediate member are connected with the ball joint, the damper device cannot receive horizontal load affecting to the wheel (lateral force and longitudinal force). As a result, two connecting points for connecting the upper arm and the vehicle body are required as well as in the double wishbone type suspension, which restricts the layout.